1. Field of the Invention
The present invention relates to the construction of a motorcycle engine provided with a cooling device.
2. Description of the Prior Art
It has conventionally been known in a motorcycle to arrange a radiator having a forced cooling fan at a position forwardly of an engine which is carried on a vehicle body frame and a carburetor leading to intake ports of the engine at a position rearward of the engine (see Japanese Patent laid open No. 58-188770 (188770/1983).
The prior arrangement structure requires the engine and the radiator to be arranged as close as possible in order to make it compact in size as a whole and to facilitate mounting of the same to the vehicle body frame, and it also requires piping between the engine and the radiator to be shortened. However, since the radiator is provided with a forced cooling fan at its backside and the motor portion of the fan projects toward the engine, the motor portion interfers with the engine and it is difficult to arrange the radiator close to the engine. When the engine is an OHC (over-head cam shaft)type straight multi-cylinder engine and is laterally placed (the alignment of the cylinders is directed laterally), casing portion of a timing transmission mechanism for driving a valve-actuating cam shaft bulges outward from a head of the engine. Therefore, it becomes more difficult to arrange the engine and the radiator at positions adjacent to each other. Moreover, the bulged casing portion stands as an obstruction in front of a carburetor, the travelling wind is difficult to hit the carburetor, which causes a rise in temperature of the carburetor, adversely affecting the intake efficiency of the engine.